ou can connect a potentiometer to the analog module 6ES7 331-1KF0.-0AB0 as follows.
* Connect the potentiometer pick-off to terminal M+ of the channel concerned.
* Connect a terminal point of the potentiometer to terminal M- of the input channel.
* Then terminals S- and M- of the connected channel are connected to each other.
Fig. 1: Potentiometer connection for resistance measuring
* You can connect potentiometers of up to 6 KOhms.
* If a variable input voltage is supposed to be formed with the potentiometer, the potentiometer pick-up must be connected to U+ and the M side of the potentiometer to M- of the module.
More information is available in the manual "SIMATIC S7-300 Programmable Controller Module Specifications " in Entry ID http://support.automation.siemens.com/WW/view/en/8859629